This invention is related to hydraulic braking systems for vehicles, especially heavy work vehicles, of the type having emergency brakes in addition to the service brakes used in normal operation and more particularly, to a hydraulic control valve for actuating both the emergency and service brakes systems.
A significant advantage of the invention is that both the service brakes and emergency brakes are actuated by the operator using the same brake pedal. Thus, in the event of a service brake failure, the operator attains the use of his emergency brakes by doing nothing more than his instinctive reaction to such an emergency--push the brake pedal harder. This probably also reduces reaction time since the operator need not reach for a separate control. Others have provided braking systems wherein a single brake pedal actuated both emergency and service brake systems. For example, U.S. Pat. Nos. 3,424,281, 3,463,276, and 3,926,282 illustrate such systems. Most of these require a loss of hydraulic pressure to the service brakes and/or overtravel of the brake pedal for the emergency brake to be actuated. However, hydraulic pressure loss is not the only way service brakes can fail.